Pioneer A-838

Commentary

This pre-main amplifier is designed with no vibration and no resonance and incorporates new technologies such as a clean ground system.

A clean ground system is used to shut out harmful noise current generated in the power supply and large current section from the electric circuit.
The power transformer and heat sink, which are sources of noise, are isolated from the chassis to prevent noise from entering the signal path. In addition, the contact points between the circuit and the chassis are connected at appropriate points to provide a bypass for returning noise current to the noise source so that noise does not enter the signal current.

Direct Construction II is used to shorten the signal path and prevent signal degradation and interference. While inheriting the conventional direct construction technology, the power amplifier board and the main volume board are integrated to greatly reduce the number of wiring steps and realize a signal path length of 85 cm.
The input block has a structure in which the input selector and main volume are mechanically controlled remotely to minimize the signal path.
In addition, by turning on the source direct switch, the input signal does not flow to the front panel at all, so you can enjoy a purer sound.
The power amplifier block is laid out along the signal flow so that the output of the power stage is directed straight to the speaker block and the distance from the power supply is minimized.
In order to minimize the length of the speaker block, the speaker terminals are directly attached to the circuit board on which the relay is attached.

In order to eliminate vibration and resonance, we are focusing on the elucidation of the vibration transmission mechanism by making full use of modal analysis by computer. Based on the results, double-sided PVC steel plates with further improved vibration damping characteristics are used for the structural materials of the shield case, bottom plate and bonnet case.
In addition, single-sided PVC steel plates are used for chassis such as rear panel, panel stay, and transformer frame to eliminate resonance of parts.
We have improved rigidity and vibration damping characteristics by using press-drawn honeycomb for the frame chassis, extruded aluminum honeycomb for the heat sink to suppress vibration and resonance of the power transistor, and large-sized honeycomb insulator filled with resin molding for the bottom.
The transformer case is made of cast iron which has excellent shielding effect and vibration damping characteristics and has almost no resonance frequency. In addition, pitch material with good thermal conductivity is filled between the case and the transformer body, and heat radiation fins are installed to prevent resistance from increasing due to temperature rise.
In addition, a balanced volume shaft that minimizes the effect of vibration is used, and a system that balances the weight in both directions around the bearing of the rotary knob of the volume prevents mechanical stress from being applied to the volume body.

In addition to the non-switching circuit type II, in which switching distortion does not occur in principle, it is equipped with the non-switching circuit type III, in which the power amplifier stage and power amplifier stage are clearly separated, improving the speaker drive performance under low load.
In addition, it stabilizes the idle current that has drifted due to temperature changes immediately after the power switch is turned on or when a large signal is input, and suppresses thermal distortion.

The Phono EQ uses a unique NF-CR type that combines the wide dynamic range of the NF type with the excellent frequency characteristics of the CR type.

By using the Phono equalizer switch, you can turn off the circuit when you are not listening to a record, thus reducing the generation of unwanted noise.
Also equipped with a V function OFF switch that turns off the power of the video system while the audio source is being played back.

Uses a oxygen-free copper power cord with polarity display that takes into consideration the effect of external noise, and uses nickel phosphorus plating for the power plug that reduces non-linear strain.
In addition, the input / output terminals are gold-plated, and the speaker terminals are of a vise type capable of supplying low-loss current.

The rotary knob uses solid aluminum shavings.

The video system is equipped with an input Route 3 and an output Route 3, allowing mutual dubbing.
To prevent the video system from adversely affecting the audio system, a dedicated power transformer is installed for the video system and the circuit and ground are separated.

Model Rating

Type	Stereo pre-main amplifier
Amplifier Unit
Rated Output (20 Hz to 20 kHz, Both Channel Drive)	180W + 180W (4 Ω, 0.005%) 150W + 150W (6 ohm, 0.003%) 120W + 120W (8 Ω, 0.003%)
Damping factor (1 kHz, 8 Ω)	200
Input Sensitivity / Impedance	Phono MM : 2.5mV/50k Ω Phono MC : 0.2mV/100 Ω CD, Tuner, VDP, VCR, Tape : 150mV/50k Ω
Phono maximum allowable input (1 kHz, 0.008%)	MM:200mV MC:19mV
Output Level / Impedance	Tape Rec, VCR Rec : 150mV/2.2k Ω
Frequency characteristic	Phono MM : 20 Hz to 20 kHz ± 0.2 dB Phono MC : 20 Hz to 20 kHz ± 0.3 dB CD, Tuner, Tape : 1 hz to 150 khz + 0 to 3 db
S/N ratio (IHF, A-network Short circuit)	Phono MM:89dB(2.5mV) Phono MC:71dB(0.25mV) CD, Tuner, VDP, VCR, DAT/Tape1, Tape2 : 110 dB
<Composite Video Part>
Input Sensitivity / Impedance	VDP, VCR1, 2, TV/AUX : 1Vp-p/75 Ω
Output Level / Impedance	Monitor, VCR1, 2 : 1Vp-p/75 Ω
DG	Not more than 2%
DP	2 degrees or less
Frequency characteristic	10 Hz to 10 MHz + 0 -1dB
Signal-to-noise ratio	60 dB or more
S-Video Terminal Unit
Input Sensitivity / Impedance	VDP, VCR1, 2 Luminance Signal : 1Vp-p/75 Ω Color Signal : 0.286Vp-p/75 Ω
Output Level / Impedance	VCR1, 2, Monitor Luminance Signal : 1Vp-p/75 Ω Color Signal : 0.286Vp-p/75 Ω
Luminance signal frequency characteristic	10 Hz to 10 MHz + 0 -1dB
Signal-to-noise ratio	60 dB or more
<General>
Power supply voltage	100 VAC, 50Hz/60Hz
AC outlet	Power switch interlock : 2 systems (200W) Power switch not linked : 1 system (100W)
Power consumption (Electrical Appliance and Material Control Law)	365W
External dimensions	Width 459x Height 173x Depth 471 mm
Weight	28kg